Smoking addiction may be inherited

Smokers may soon benefit from new drug treatments that fight nicotine addiction based on genetic research, according to a recent US study.

The researchers found that a gene known as CHRNA5 was responsible for some of the addictive aspects of tobacco use.

The gene the researchers studied controls part of the brain's actual reception of nicotine, acting as a DNA blueprint for a 'lock' into which nicotine fits like a 'key'.

The human body feels pleasure from smoking because nicotine is active inside the brain at particular dosages, triggering specific amounts of other neurotransmitters, such as dopamine.

If the amount of nicotine is too small, people end up wanting more, and if the amount is too large, people feel unhealthy.

Unfortunately, a large sector of the world population have a particular genetic mutation of CHRNA5 that makes a slight change to the receptor.

In these people, the behaviour of the alpha5 portion of the CHRNA5 receptor is slightly different, and the experience of having too much nicotine almost never comes.

Instead, the brain's craving is almost unlimited, and quantities of nicotine that would lead to nausea or dysphoria in others have the opposite effect, leading to chain-smoking.

Lead researcher Paul Kenny, at the Scripps Research Institute in Florida, said that people with the alpha5 mutation were likely to be far less sensitive to the averse properties of nicotine, and more susceptible to addiction.

Jon Lindstrom, a neuroscientist at the University of Pennsylvania, said that the current study had important implications for new approaches to quitting smoking.

He said that people may need to target more than one receptor, however, if they wished to develop effective smoking cessation drugs.

In the USA, up to 35% of all people may be genetically predisposed to nicotine addiction.

Lindstrom, who plans to take part in follow-up studies with Kenny's group of researchers, said that nicotine influenced complex brain circuits involved in reward and memory.

He said that nicotine helped people concentrate as well as helping them stop worrying about things, and that people who quit smoking found it hard to live without the aid of nicotine.

Wearing nicotine patches may in fact increase people's nicotine cravings, augmenting an addiction that already accounts for about 10% of all adult deaths worldwide, killing millions of people annually.

Lindstrom said that making people more averse to large doses of nicotine might help them to stop smoking once and for all.